Butsuri
Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
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Preface
Contents
Researches
  • Statistical Mechanics of Protein Design
    Tomoei Takahashi, George Chikenji, Kei Tokita
    Article type: Researches
    2025 Volume 80 Issue 3 Pages 116-120
    Published: March 05, 2025
    Released on J-STAGE: March 05, 2025
    DOIhttps://doi.org/10.11316/butsuri.80.3_116
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    We approach the protein design problem, which is the inverse of predicting protein three-dimensional structures, through statistical mechanics. We formulate the protein design problem using Bayesian learning. As a result, our method successfully designs relatively small two-dimensional (2D) lattice hydrophobic-polar (HP) models and some larger 2D lattice HP models. The calculations are faster than in previous studies because our proposed Bayesian design method skips the calculation of the partition function of conformational space. This result is nearly the same for both the Markov-chain Monte Carlo method and the cavity method, the latter of which is a generalization of the mean-field approximation. Additionally, we propose a prior probability distribution for amino acid sequences as a hypothesis of protein sequence evolution.

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  • Spin-Space-Group Analysis of Emergent Responses of Magnets
    Hikaru Watanabe, Takuya Nomoto, Ryotaro Arita
    Article type: Researches
    2025 Volume 80 Issue 3 Pages 121-125
    Published: March 05, 2025
    Released on J-STAGE: March 05, 2025
    DOIhttps://doi.org/10.11316/butsuri.80.3_121
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    Recent studies have identified the nonrelativistic spin-momentum locking of antiferromagnets where crystalline sublattice and spin degrees of freedom are coupled to each other. The order-induced spin-charge coupling gives rise to various emergent responses, such as the electrical spin-current generation. These phenomena do not rely on the relativistic spin-orbit coupling, and thus its essence is not captured by the conventional magnetic symmetry analysis with the magnetic space group. To this end, we present the spin-space-group symmetry analysis. We clarified that the symmetry unique to the spin space group, such as the spin-only group and spin-translation group, realizes spin-inactive but orbital-active physical properties, in stark contrast to the known collinear antiferromagnets.

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Experimental Developments
  • Nuclear Spin Polarization―Dynamic Nuclear Polarization Using Photo-Excited Triplet Electrons
    Kenichiro Tateishi, Tomohiro Uesaka
    Article type: Experimental Developments
    2025 Volume 80 Issue 3 Pages 126-133
    Published: March 05, 2025
    Released on J-STAGE: March 05, 2025
    DOIhttps://doi.org/10.11316/butsuri.80.3_126
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    Nuclear spin polarization and techniques to improve it are reviewed. Although the conventional Dynamic Nuclear Polarization (DNP) technique can polarize nuclear spins up to 100%, it has been difficult to use it as a polarized target for unstable nuclear physics. We have therefore developed a low-field and high-temperature polarization technique using Triplet-DNP. Using pentacene as a polarizing agent, the hyperpolarized electron can be produced independent of experimental conditions, and 1H polarization of 40% was achieved at 0.65 T and room temperature. We also constructed a polarized target to perform as the neutron spin filter, and to measure the spin-orbit potential of neutron-rich helium isotopes.

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